The present invention relates to a milking installation and to a method for the reduction of noise emissions in a milking installation.
Previously disclosed milking installations consist of numerous component parts, the interaction of which facilitates the milking of cows, sheep or goats. A vacuum is created by means of a vacuum pump unit, which comprises a vacuum pump and its drive motor. This vacuum is applied in an air line, to which the actual milking device is connected. A vacuum equalization tank is generally provided in order to maintain a stable vacuum. The vacuum equalization tank makes a certain volume of air available, whereby initial equalization of fluctuations in the vacuum can take place. Further equalization takes place by means of a vacuum control valve. By opening and closing the vacuum control valve, the admission of outdoor air into the system is controlled in such a way that the vacuum is maintained at a stable level.
At least one pulsator is also provided in a milking installation. As a rule, the pulsator consists of one or two independent, pneumatically or electrically directly (armature) or indirectly (membrane) activated valves, with the help of which in the milking device itself continuous alternation takes place between low pressure and normal pressure, which affects the actual milking procedure. The milking device consists of four teat cups and one collector piece. This is placed on the teats of the animal to be milked. The milking device has two connecting hoses. There is thus a pulsation hose, which is connected to the air line via the pulsator, and via which the milking procedure consisting of a suction phase and a pressure release phase is effected.
The milking device also exhibits a milk hose, by means of which the milk is led away. This discharges either into the milk pail or into a milk transport pipe, the so-called milk pipe. The milk is conveyed via this milk pipe to an end unit, the so-called milk collection vessel. The milk flows into this vessel and, on reaching a specific level, is led away by means of a milk pump to the actual milk storage tank, in which the milk is cooled and stored until collection. Finally, a safety separator is also provided. This is connected to the milk collection vessel. In the event of failure of the milk installation control system, the milk collection vessel may become overfull. The milk then flows into the safety separator. A float valve is raised here in sequence to close the outlet and the connection to the vacuum equalization tank. Operation of the milking installation is interrupted in this case. The milk in the safety separator must be drained manually and disposed of.
Milking installations of this kind are a source of constant noise when they are in operation. This noise derives from various elements of a milking installation. The elements responsible for generating the principal noise and vibrations can be mentioned.
Let us first make reference here to the vacuum pump unit. On the one hand this generates noise, for example in the form of engine noise, which is propagated through the air and which lies in the audible range. However, the noise is also propagated in the air pipe. Finally, because the air pipe is attached to the milking framework via flexible connections, the entire milking framework is caused to oscillate. The oscillations can also be transmitted in this way to living beings that are associated with the milking framework. The noise generated by the vacuum pump unit can also be propagated via the fabric of the building in the form of so-called structure-borne noise. This can ultimately lead to the oscillations being distributed through the entire structure of the building. A further unpleasant side-effect can also arise as a result of noise reflections occurring in the vacuum tank and in the air pipes, which contribute to multiplication of the noise frequency. It can also result in interference phenomena, whereby the amplitudes of the disturbances are amplified. This could lead to a frequency range being reached, which corresponds to the natural frequency of the milking parlour framework and is sufficiently powerful to excite this, too.
The pulsators must be regarded as a further source of disturbance. Pulsators today are electrically operated as a rule. The directly operated pulsators exhibit an armature valve, the impact of which in the end position provokes a heavy, jerking impulse. This impulse is conducted in the form of structure-borne noise directly into the air pipe and the milking parlour framework. The impact noise is clearly perceivable acoustically. Pulsators with indirect valve control are quieter in operation, on the other hand, because a membrane exhibits little mass. A particular disadvantage in this respect is the fact that the opening and closing movement takes place very rapidly and, in so doing, forces a powerful air blast into the air pipe, which is similarly capable of producing a disadvantageous effect. This noise emission manifests itself on the one hand via the vacuum, and on the other hand as structure-borne noise. Multiplication of the impact intensity can occur as a consequence of the parallel connection of all the pulsators. A further negative effect is that air enters the air pipe at regular intervals as a consequence of the pulsation. The vacuum is disturbed in this way, and this can trigger an opposing reaction in the sensitive vacuum control valve.
The vacuum control valve can be mentioned as the third source of noise. The vacuum control valve varies the admission of air so that the vacuum can be maintained at a constant level. The velocity of the arriving air is dependent on a variety of factors. It is thus dependent on the quality of manufacture of the valve, but also on the location of the milking installation above sea level, and thus on the atmospheric pressure. At an altitude of 1500 m, the velocity of the arriving air can even reach the speed of sound. As soon as the speed of sound is reached, however, stall conditions occur briefly. This condition is associated with a whistling noise. The entry of air into the vacuum system after opening the control valve is perceived in any case, however, since the air enters the vacuum system relatively rapidly, so that turbulence phenomena and oscillations occur. In addition, the milk pump is also one of the principal sources of noise.
The generated noises, vibrations and oscillations are distributed through the entire milking installation. They are ultimately also perceived by the animals, both on the basis of their transmission through the air, and on the basis of structure-borne noise, for example via the milking parlour frameworks against which the animals lean during the milking procedure. High-output animals are extremely sensitive, however, and react even to the slightest disturbances by giving a reduced milk yield. The general well-being of the animals is also susceptible to disruption in this way and, in extreme cases, an arrested milk flow can lead to udder inflammation.
The current state of the art has until now offered only two approaches to the reduction of these noise and vibration effects. It is known that the application of a rubber covering to all pipes, and in particular the pipes constituting the air pipe, reduces the propagation of noise in the pipe. Another approach is revealed in the playing of music, in particular classical music, in the milking area, which is claimed to produce an increase in the flow of milk from the animals and to improve their psychological state. However, the previously disclosed approaches to finding a solution are ultimately unsatisfactory and insufficient.
Further problems are associated with the vacuum control valve in conventional milking installations. Thus, a consequence of the pressure wave generated by the pulsator is that the sensitive vacuum control valve begins to oscillate, in spite of the fact that the vacuum remains stable from an overall point of view. As a result of this, too much air is supplied to the system as a whole, which must be removed by the vacuum pump. The vacuum can fall significantly as a result of this, in fact within a period of ca 1 second. However, the constant operation of the vacuum pump causes the vacuum to rise again relatively quickly. Vacuum instability prevails within the system, in spite of this, and this should be avoided in order to ensure a good milking procedure.